a) Field of the Invention
The present invention relates to a process for manufacturing a composite material from a mixture comprising:
a binder made up of two components capable of reacting with each other, at least one of these two components being in a liquid form; PA1 at least one filler; and PA1 reinforcing fibers. PA1 a binder made up of two components capable of reacting with each other, at least one of these two components being in a liquid form; PA1 at least one but preferably several fillers; and PA1 reinforcing fibers such as asbestos fibers, asbestos-derivative fibers, cellulose fibers, glass fibers or plastic fibers, the binder being selected from the group of binders made of the following components: PA1 hydraulic cement and water; PA1 potassium and sodium silicate and water; PA1 colloidal silica and water; and PA1 organic resins and hardeners or catalysts for such resins, PA1 the filler(s) and fiber(s) being selected to be chemically compatible with the binder and to give the composite material some predetermined structure and properties. PA1 impregnating all of the liquid component of the binder into an absorbing substance compatible with the binder, filler(s) and fibers, this absorbing substance being vermiculite, perlite or any similar material and constituting the filler or being a part thereof; PA1 mixing the absorbing substance impregnated with the liquid component of the binder with the solid component of the binder, if any, with the filler(s) and with the fibers in a mixer for a period of time sufficient to obtain the requested mixture in a semidry and homogeneous form, in which the fibers are entirely dispersed; PA1 introducing the semi-dry mixture into a mold of a press and compressing the mixture under a pressure and for a period of time depending on the composition of the mixture and the predetermined properties of the composite material to be obtained; and PA1 subjecting the compressed material to ageing and hardening as a function of the kind of binder being used, in order to obtain the desired composite material.
b) Brief Description of the Prior Art
The manufacture of composite materials from mixtures of the above mentioned type, has been known for a very long time.
In the particular case of asbestos cement which is one of the composite materials that has the most widely been used throughout the world since the beginning of this century, the different components of the mixture used as starting material, are:
a binder consisting of hydraulic cement and water;
fillers; and
asbestos fibers used as such or in combination with other fibers, such as cellulose fibers.
In this particular case, the binder usually comprises a hydraulic cement, which may consist of Portland cement. The binder has a solid part and a liquid part, this liquid part being water. The solid part may consist of cement only, which is mixed with water and subject to ageing under ambient pressure and temperature. The solid part of the binder may also consist of a mixture of Portland cement with silica sand, usually in a ratio of 60 to 40. The mixture is subjected to ageing under hydrothermic condition (autoclaved steam curing).
The fillers that are used in the starting mixture for the manufacture of asbestos cement, usually consist of dyes for coloring the finished product, and of inert fillers whose purpose is to reduce the amount of raw material being used and thus reduce the cost of the finished product. These inert fillers may consist of chunks of finished product rejects, sand, calcium carbonate, clay, perlite, etc...
The reinforcing fibers that are used, consist of asbestos fibers of commercial grade, of the chrysotile, crocidolite or amosite type. For some application, cellulose fibers may also be mixed with the asbestos fibers.
The processes that are presently being used for the manufacture of pieces of equipment made from such a composite material, viz. asbestos cement, starting from the above described mixture, are, on the one hand, a process named after its inventor, Mr. HATSCHEK, which process is commonly used for the manufacture of sheets, and a process also named after its inventor, Mr. MAZZA, for the manufacture of sleeves and pipes.
In both of these processes, an aqueous suspension of asbestos fibers and hydraulic cement, having a concentration of about 3 to 10% by weight of solids, is filtered into a rotating cylindrical sieve. The sheet of dry material that is recovered on the rotating sieve is placed on a felt conveyor and wound up onto a calendering cylinder until a sleeve of the desired thickness is obtained. To produce sheets, the dry substance that is wound up onto the calendering cylinder is cut, unwound and subsequently subjected to forming and ageing. To produce pipes, the dry substance wound onto the calendering cylinder is subjected to ageing, then removed from the cylinder and subsequently treated, if desired.
The above mentioned processes call for substantial investment in machinery and space. Usually, the HATSCHEK machines are capable of producing from 3 to 12 tons per hour, and therefore cannot be used for manufacturing products in small quantities, but rather in applications requiring high specificity.
Therefore, other processes have been proposed for processing smaller amounts of asbestos cement. An example of such a process is disclosed, by way of example, in British patent No. 1,083,809.
Over the last decades, asbestos fibers have been banned from different countries because of alleged health hazards. As a result, other types of composite materials have been developed, starting from mixtures that can be processed as disclosed hereinabove. The compositions of these other mixtures are very similar to that of asbestos cement, except that the reinforced fibers that are used are not made of asbestos but of other material. By way of example, reference can be made to U.S. Pat. No. 4,414,031 which discloses a fiber-reinforced cement whose reinforced fibers are made of polyacrylonitrile, and U.S. Pat. No. 3,974,024 which discloses a process of manufacture glass fibers cement.
In the cases of composite materials making use of inorganic binders other than cement and water, such as sodium or potassium silicate and water, or colloidal silica and water, other processes have been developed.
In the cases of composite materials making use of organic binders, such as, for example, polyester or epoxy resin and a catalyst or hardener, other processes have also been developed.
As a matter of fact, for each existing composite material, there is one very specific process of manufacture, this process being, most of the time, restricted to the said very composite material. In other words, a process for use to manufacture a given amount of a particular composite material can very seldomly be used to manufacture other composite materials. Sometimes, such a process cannot even be used to manufacture the same composite material if the amount of this composite material to be manufactured is increased or reduced.
Thus, by way of example, the composite material whose formulation is given in U.S. Pat. No. 3,974,024 cannot be manufactured by the process disclosed in U.S. Pat. No. 4,414,031 and vice versa.
Moreover, the processes useful for mass production and making use of a substantial amount of water, such as the HATSCHEK process, often lead to segregation and sedimentation of the materials being processed, when one tries to process some other particles or fibers, or tries to reduce the amount of materials to be processed.
Similarly, processes like the one disclosed in British Pat. No. 1,083,809 for use to process a mixture containing a small amount of moisture, often lead to the formation of "chunks" or aggregates of fibers in the mixture if use is made of other kind of fibers or other binders, or, more particularly, if one tries to increase the amount of mixture being processed at one time.